Method for operating a wind energy converter, control device for a wind energy converter, and wind energy converter.
The present invention relates to a wind energy converter.
Wind energy can be converted into useful forms, such as electricity, by a wind energy converter that includes a rotor, e.g. a low-speed propeller, coupled to a generator. Since the speed of wind at a given location in general fluctuates with changing weather conditions, conventional wind energy converters are typically operated with variable rotor speed in order to achieve a high aerodynamic efficiency of the rotor at different levels of wind speed.
In some implementations, to supply electricity into an electric power grid, it is advantageous to use a constant-speed generator such as a synchronous generator directly connected to the grid for power transmission. In addition to economic benefits, the quality of the electric power fed into the grid is usually higher without a power converter, which can be expensive. Furthermore, the constant speed generator can be operated at a medium voltage level such that no additional transformer is needed.
DE 10 2005 054 539 B3 discloses one example of a wind energy converter including a rotor and an electrical generator for direct connection to an electric power grid. In this example, the rotor and the generator are coupled by a variable-ratio gear system that includes a hydraulic component for controlling the gear ratio of the variable-ratio gear system. As a result, the wind energy converter operates at a variable rotor speed according to the speed of wind while driving the generator at a constant speed.
In the above example, while aerodynamic losses of the wind energy converter can be reduced by adjusting the rotor speed to changes in the speed of wind, a substantial portion of the power is transported from the rotor to the generator via the hydraulic component of the variable-ratio gear system. As hydraulic components generally suffer power losses by leakage flow, friction losses etc., the overall efficiency of the wind energy converter is reduced due to the power losses in the hydraulic component of the variable-ratio gear system.